This code was calling `sort_unstable_by`, but failed to impose a total order on
the initial spans. That resulted in unpredictable handling of closure spans,
producing inconsistencies in the coverage maps and in user-visible coverage
reports.
This patch fixes the problem by always sorting closure spans before
otherwise-identical non-closure spans, and also switches to a stable sort in
case the ordering is still not total.
These changes were made by manually running `rustfmt` on all of the test files,
and then manually undoing all cases where the original formatting appeared to
have been deliberate.
`rustfmt +nightly --config-path=/dev/null --edition=2021 tests/run-coverage*/**/*.rs`
Prior to #114875, these tests were very sensitive to lines being added/removed,
so the migration to `run-coverage` in #112300 tried hard to avoid disturbing
the existing line numbers. That resulted in some awkward reshuffling when
certain comments/directives needed to be added or moved.
Now that we don't have to worry about preserving line numbers, we can rearrange
those comments into a more conventional layout.
